The present invention relates to a process for the manufacture of hydroxylammonium salts by catalytically reducing nitric oxide with hydrogen in a dilute aqueous mineral acid in the presence of a suspended platinum catalyst at an elevated temperature, wherein the reaction is carried out in a vessel consisting of certain specific materials.
In the manufacture of hydroxylammonium salts by catalytically reducing nitric oxide with hydrogen in a dilute aqueous mineral acid in the presence of a suspended platinum catalyst at an elevated temperature, a problem which arises is that the acid reducing reaction mixture is extremely corrosive. Only a limited selection of materials sufficiently resistant to corrosion is available. Plastics, e.g. polyvinyl chloride, polyethylene, polypropylene and polytetrafluorethylene, synthetic rubbers and natural rubbers have proved suitable. Equipment lined with enamel, graphite, platinum or tantalum has also proved suitable for such corrosive media.
The disadvantage of using such materials for constructing the reactor are on the one hand the high cost and difficulty of processing the materials, and on the other hand unsatisfactory properties such as fragility, embrittlement on aging, sensitivity to impact and shock, and low mechanical strength. These properties make it particularly difficult to construct reactors for the manufacture of a hydroxylammonium salt if the synthesis is to be carried out under pressure.
A number of commercial steel alloys of high mechanical strength and good corrosion resistance have also proved unsatisfactory for use in conjunction with the synthesis of hydroxylamine by catalytically reducing nitric oxide in an aqueous mineral acid. Chromium-nickel steels containing added titanium (material 1.4541) undergo corrosion under the influence of the reducing, strongly acid aqueous reaction medium. Other corrosion-resistant chromium-nickel steels, containing added molybdenum as well as copper, which are particularly stable to dilute sulfuric acid under normal use conditions, also exhibit corrosion. However, a particular disadvantage is the adverse effect, on the course of the reaction, of the constituents of the metal alloys which pass into solution.